Traditionally, coil components such as inductors, transformers, and chokes are used in a wide variety of applications such as home electric appliances, industrial apparatuses, and vehicles. A coil component is composed of a magnetic core and a coil wound around the magnetic core. In recent years, as a result of downsizing of power supplies for electronic devices, there has been a strong demand for compact low-profile coil components operable even with a large current, and powder magnetic cores produced with a metallic magnetic powder, which has a relatively high saturation magnetic flux density, are increasingly used for such coil components. For example, a soft magnetic alloy powder such as an Fe—Si alloy powder is used as such a metallic magnetic powder. Structures used for coil components include a common structure in which a coil is wound around a powder magnetic core obtained through pressing; and a structure obtained by integrally molding a coil and a magnetic powder so that the compact and low-profile requirements can be satisfied (coil-sealed structure).
Powder magnetic cores obtained through the compaction of a soft magnetic alloy powder such as an Fe—Si alloy powder have high saturation magnetic flux density as compared with oxide magnetic materials such as ferrite. However, the soft magnetic alloy powder used for such powder magnetic cores has low electrical resistivity (specific resistance). Therefore, methods of improving the insulation between soft magnetic alloy particles are used, such as methods of forming an insulating coating on the surface of soft magnetic alloy particles. For example, Patent Document 1 discloses a method of heat-treating, at 400° C. to 900° C., a compact including a group of particles of a soft magnetic alloy including Fe, Si, and Cr or Al, which is a metal element more vulnerable to oxidation than Fe, and also discloses a magnetic including particles bonded together through an oxide layer formed by the heat treatment. The object thereof is to obtain a magnetic core with high magnetic permeability and high saturation magnetic flux density without the need for high pressure during molding.
Patent Document 2 discloses an example using an Fe—Cr—Al magnetic powder, which can produce, by itself, a high-electric-resistance material capable of serving as an insulating coating.